Raycasting with opaque isosurfaces in nonregularly structured CFD data

Direct volume rendering (DVR) is becoming more and more useful fort he graphical analysis of computational fluid dynamics (CFD) data, because of the extremely huge datasets that are generated with today's supercomputers. However, only semi-transparent visualisations have been produced via DVR from nonregularly gridded simulation data so far. Such images provide no information about the data distribution in the viewing direction. This paper reports our realisation of opaque and combined semi-transparent/opaque raycasting in nonregular grids. We emphasize on the mapping process, on the colour accumulation, and on the shading of isosurfaces. The generated images provide both holistic information and cues about the spatial data distribution in the viewing direction. We use the same interpolating functions in the visualisation algorithms as they are used in the data generation with the Finite Element method. Therefore, the rendered isosurfaces reveal interesting features that cannot be seen when isosurfaces are extracted directly with simplier algorithms.